The present invention relates generally to digital printing technology, and more particularly to techniques for aligning print heads on a print head carriage of a printer.
Printing technologies have advanced dramatically over the last few decades. For many years, the standard technology for printing large quantities of the same prints has been the domain of offset printing. Offset printing involves the transfer of an inked image from a plate to a rubber blanket, then to the printing surface. In large industrial offset presses, the plates and rubber blankets are wrapped around rollers which allows for high-speed production of thousands of copies of a printed image. Offset printing presses embody direct contact printing in that the components of the press (for example, the rubber blanket) directly contact the paper on which the image is printed.
In the background of the industrial realm, inkjet printing began to take hold as an inexpensive digital printing technology used mainly in the home and small office domains. Inkjet printing technology operates by ejecting miniscule ink droplets from nozzles of a print head device directly onto the surface of a printing substrate without the device coming into contact with the printed surface. Inkjet has the significant advantage that it does not require physical plates to be created for every image to be printed, nor for direct contact components, such as the rubber blanket, which requires ongoing maintenance. Inkjet printing therefore can be far more economical when printing a single or few copies of a particular print. However, in its early days, inkjet printing was typically much slower than offset printing due to limitations of the hardware. Furthermore, because inkjet printing prints a digital image, limitations on the obtainable printed resolution often made offset printing or laser printing the better choices over inkjet for applications requiring very high quality printing.
More recently, inkjet printing technologies (and various related non-contact printing technologies) have advanced to the forefront of industrial digital printing. Improvements in print head technology and print head carriage configurations have allowed for increased print resolution, and additionally throughput has increased. The advantages offered by inkjet printers, including purely non-contact printing, which reduces wear and tear on printer components and makes for a much cleaner printing environment requiring less process maintenance, along with the elimination of the need to create physical plates for each image, makes inkjet not only a viable printing approach for industrial printing, but may even make inkjet printing the favored solution.
In general, inkjet printers utilize one of two methods for printing: multi-pass (or “multi-scan”) printing and single-pass printing. In multi-pass printing, the print substrate (i.e., the object on which the image is to be printed) is advanced in a forward “feed” direction along a “feed axis”, while a print head carriage carrying a number of print heads is reciprocated in a scanning direction along a scan axis that is perpendicular to the feed axis. The print head carriage traverses the print substrate in multiple passes back and forth along the scan axis as the print substrate advances along the feed axis.
In single-pass printing, the scan axis and the feed axis are the same, where the print head carriage remains in a fixed position while the print substrate is advanced past the print head nozzles in a single pass to complete the image. Alternatively, the print substrate remains in a fixed position while the print head carriage advances across the print substrate in a single pass to complete the image.
Regardless of whether the printer is configured for multi-pass printing or single-pass printing, the print head carriage in an industrial inkjet printer will typically carry many individual print heads. For example, as will be described in more detail hereinafter, a print head carriage may carry dozens of print heads simultaneously. Each print head mounted on the print head carriage contains a plurality of individual nozzles through which ink is ejected during the printing process. For any given print head, the print head nozzles are precision-aligned in linear rows by the manufacturer to be within a specified distance plus/minus a specified tolerance with respect to each other. However, with respect to the edges of the print head package (e.g., the housing, cover, and mounting plate), the nozzles are not necessarily as accurately aligned. Furthermore, when a print head is mounted onto a print head carriage, its seating on the carriage may skew the alignment of the nozzles with respect to the carriage and/or with respect to the nozzles of other print heads seated on the carriage.
Precise alignment of the print heads on the print head carriage is required for printing accuracy and quality. As a result, the alignment of the print heads must be checked and adjusted prior to using the print head carriage for printing. On a print head carriage which carries multiple print heads, the alignment of the nozzles must also be performed so that nozzles across different print heads also align to each other. On a print head carriage which carries many print heads, this can take a significant amount of time. In addition, since the nozzle pitch on a print head is typically on the order of tens of microns, the print head alignment process can be quite tedious and time-consuming even for the skilled technician.
Due to repeated use of the print heads by the printer, the print heads can wear out or clog over time, and therefore individual print heads on the carriage need to be replaced intermittently. After replacement of a print head, the replacement print head needs to be aligned on the carriage to ensure accurate alignment of its nozzles relative to the nozzles of the other print heads on the carriage. Print head replacement requires removal of the print head carriage and traditionally involves the iterative process of printing of test patterns on paper, measuring the alignment of the printed dots on the paper, and adjusting the alignment of the print head. This process can take hours or even up to days of a technician's time to replace and align or re-align the print heads on the carriage. Unless another print head carriage is available and ready to go with previously-aligned print heads, the printer becomes unavailable for use during the duration of the replacement and alignment process. In a production environment, this may be unacceptable.
It would therefore be desirable to have better processes and systems for aligning print heads on a print head carriage.